Anterior cruciate ligament (ACL) injury is prevalent and often leads to instability, quadriceps muscle weakness and osteoarthritis. (OA) Many of those with chronic ACL deficiency have evidence of knee OA years after ACL rupture. Weakness and instability experienced by those who do not compensate well for ACL deficiency (non-copers) independently lead to compensation strategies that could precipitate or worsen knee OA. These poor compensation strategies do not uniformly resolve after surgical reconstruction and those who undergo reconstruction also have an increased risk of developing knee OA. The overall goal of this work is to determine whether effective rehabilitation programs to dynamically stabilize the knee reduce the adaptations that lead to osteoarthritis in a population at great risk for the development of knee OA. Eighty individuals with ACL rupture who are scheduled for surgery will be randomly assigned to a group that includes a form of neuromuscular training called perturbation training, or a standard group. They will be evaluated before and after surgery using motion analysis and radiography. In vivo measures of kinematics, kinetics, tibial translation and EMG based models of joint compression will be used for comparison. This randomized trial is designed to demonstrate that, after preoperative rehabilitation that includes perturbation training, movement patterns adopted by non-copers: 1) demonstrate improve joint stability and reduced muscle cocontraction, 2) persist after reconstruction and 3) result in better functional outcomes after reconstruction and 4) lead to the development of less knee pain and OA over time than standard preoperative treatment strategies. The information derived from this project will provide valuable insight into the management of the approximately 100,000 Americans who rupture their ACLs each year and undergo reconstructive surgery. More importantly, if the perturbation training program's ability to induce dynamic knee stability actually results in joint protection, its application to others at risk for the development knee OA may help reduce the incidence of this disabling clinical condition.